Optimal placement of storage volumes is desirable in an effort to maintain desired application response times. This may be a time-consuming process, and storage administrators are often too busy dealing with other issues to perform proactive optimization. One aspect of optimization is utilization of storage volumes selected from appropriate tiers of storage.
Tiers of storage, in this context, is common industry terminology that represents performance/cost of various forms of storage. Although precise definitions for the various storage tiers are elusive, since conventions may vary from one provider to another, Tier 1 storage is generally fast, accurate storage supported by high-speed disk systems that are often associated with premium pricing. Tier 2 storage systems provide adequate performance in applications where high-speed data interchange is not generally required, but large amounts of data may be involved. Tier 2 storage systems are generally available at a lower cost than Tier 1 storage systems. Tier 3 storage systems are often directed toward storage of data that are accessed infrequently, but nonetheless require reasonable availability. Tier 3 storage is generally available at a lower cost (reflecting lower performance) than the higher level storage tiers. The numbering system for storage tiers is often not intuitive, since a commonly-used convention may refer to high-performance storage as Tier 1 and lower performance storage as Tier 3, while clinging to the notion that Tier 1 storage is a “higher tier” than Tier 3, even though it is denominated by a lower number.
By moving “hot” volumes (volumes frequently accessed with high-speed data interchange) to higher tiers of storage (such as Tier 1), desired performance can be obtained, while moving cold volumes (volumes that are less frequently accessed at lower data transfer rates) to lower tiers of storage (such as Tier 3) allows for the use of lower-performance, less costly storage solutions, leading to greater system economy. Optimal volume placement may amount to a tricky balancing act, wherein a storage administrator seeks to meet application response time requirements while at the same time using the lowest tier storage possible.